Buckle up, it's Loooore time.
Uluri's shape is not affected by the weather, but is affected by what Uluri eats. Uluri is a mimic slime, and will take on a species form after having eaten one. Not the exact form of what's been eaten, but the species in general.
Uluri cannot be microwaved. Like any slime, there is a core in there that can be damaged. Shooting microwaves into it isn't reccomended.